1. Field of the Invention
This invention relates to a profile working machine such as die-finishing grinding machine, ceramics-working grinding machine, three-dimensional milling machine or the like.
2. Description of the Prior Art
When performing working or machining to form a free-form curved surface on a work such as die machining, the working or machining is in many instances conducted by mounting a ball end mill or the like on an NC milling machine or a machining center. After such working or machining is performed, cutting tool marks are caused to remain on the thus-finished die. Hence, it cannot be used as a die without any additional machining or treatment. It has thus been required to add a further step in which such cutting tool marks are removed with a shafted grinder held by a hand while observing them. Such a manual work was prevented full automation of machining steps in profile machining work, thereby imposing a serious limitation on the profile machining work.
With a view toward solving this problem, the present inventors have already proposed in Japanese patent application No. 201487/1984 a profile working machining which permits automated working of curved surfaces of a work. The outline of this profile working machine will next be described with reference to FIGS. 9 and 10.
FIG. 9 is a side view of a working tool and a work. In the drawing, there are illustrated a table 1 of a working machine, a work 2 fixedly held on the table 1, and a working tool 3 for grinding the work 2. Letter T indicates a point of action (working point) by the working tool 3 on the work 2, while letter designates a working reaction force exerted on the working tool 3.
FIG. 10 is a system diagram of the profile working machine. In the drawing, there are shown a working tool/work system 5 which includes the table 1 and working tool 3, and a load sensor 6 for detecting a force (force components and moment components applied respectively along and about respective axes) to the working tool 3. Designated at letter is a force component detected by the load sensor 6, while indicated at letter is a moment component detected by the load sensor 6. Numeral 7 indicates a computing unit for control, which is composed of a unit 7A for outputting data on the shape of each working tool (hereinafter called "working tool shape data output unit 7A"), a unit 7B for calculating each working point and tangential plane (hereinafter called working point/tangential plane calculation unit 7B), and a unit 7C for computing each working point and working reaction force (hereinafter called "working point/working reaction force computing unit 7C"). The working tool shape data output unit 7A outputs, as a signal, data on the shape of the working tool 3, for example, a ball having a radius of such and such millimeters or a cylinder having a radius of such and such millimeters and a length of such and such millimeters. The working point/tangential plane calculation unit 7B calculates the position of the working point T and the tangential plane P.sub.t at the working point T on the basis of the data output from the working tool shape data output unit 7A and the force and moment detected by the load sensor 6. The working point/working reaction force computing unit 7C judges, based on the working reaction force detected by the load sensor 6 and the working point T and tangential plane P.sub.t calculated by the working point/tangential plane calculation unit 7B, whether the working reaction force is suitable or not for the working point T and tangential plane P.sub.t, and outputs a position signal and spatial orientation signal to correct the working reaction force .
Designated at numeral 8 is a drive and control system for respective axes, which operates upon input of the signals , . In accordance with the signals , , the drive and control system 8 controls the relative positions X and relative spatial orientations between the table 1 and working tool 3. Numeral 9 indicates displacement sensors for detecting the present positions and spatial orientations of the table 1 and working tool 3, and outputs the so-detected position signals and spatial orientation signals .
In the above construction, the working point T and tangential plane P.sub.t are always calculated by the working point/tangential plane calculation unit B, and a judgement is made to determine whether the working point T is located at a point where the working tool 3 can perform machining. When the judgement is "YES", a another judgement is made by the working point/working reaction force computing unit 7C to determine whether the present working reaction force is suitable for the working point T and tangential plane P.sub.t. When the present working reaction force is suitable, the working is continued as is. When it is not, computation is performed to determine how the relative positions and relative spatial orientations of the working tool 3 and table 1 should be corrected to adjust the working reaction force to suitable values. As a result, the working point/working reaction force computing unit 7C gives commands , the drive and control system 8 for the respective axes. Here, the commands , may generally be input in the form of target relative positions and target relative spatial orientations or in the form of degrees of displacements .DELTA.X, .DELTA. over which the relative positions and relative spatial orientations should be corrected from the present state.
As mentioned above, the above-described profile working machine can perform machining copying the profile, namely, the curved surface of the work 2 while always maintaining the working reaction force exerted on the working tool 3 at the most suitable value. Therefore, the profile working machine allows to conduct profile machining work automatically under ideal working conditions.
In general, the coordinate system of the working tool 3 is usually different from that of the load sensor 6. No particular correlation is contemplated either between both coordinate systems in the above-described conventional profile working machine. Therefore, each load component detected by the load sensor is based on the coordinate system of the load sensor 6. In order to determine the working reaction force exerted on the working tool 3, computation is required to transform the value detected by the load sensor 6 into a value under the coordinate system of the working tool 3. Since this computation is complex, the computing unit requires lots of time for its design and fabrication and correspondingly, a rather long period of time is needed to perform the computation.
The above computation includes a computation step in which the working point T and tangential plane P.sub.t are determined. This computation is more complex than the above-mentioned computation for the transformation of the coordinate system. One example of this computation is described in U.S. patent application Ser. No. 776,801 of Sept. 17, 1984, now U.S. Pat. No. 4,666,352. It will be clearly understood from the passage how complex the computation is. Moreover, the exemplified computation is limited to a simple example in which the working tool 3 is spherical. Where the working tool 3 has various shapes other than sphere, the computation of the working point T and tangential plane P.sub.t will apparently become more complex. Correspondingly, the computing unit of the working point T and tangential plane P.sub.t requires still more manpower and time for its design and fabrication and at the same time, their computation requires substantial time.
As has been described above, the conventional profile working machine contains, in its control loop, a computation step which requires significant computing time. The conventional profile working machine is therefore accompanied by such drawbacks that its computing unit requires a high fabrication cost and since its responsibility, which is needed for the control of forces, is reduced, it cannot achieve any high working speed.